The quality of many materials is highly affected by the temperature at which the materials are stored and distributed. For example, there has been a strong trend by foodstuff producers towards producing chilled, ready-cooked dishes that preferably are retained at a temperature of about 0.degree. C. (32.degree. F.) as long as possible from the moment of production until the consumer buys the product in the shop. The essential thing is that the product does not reach a temperature below its freezing-point which may be lower than 0.degree. C. if freezing-point lowering substances, such as salt, are included in the product. In fact, a slow refrigeration at a few degrees below zero deteriorates the structure and certain quality properties of the product. Likewise, flower and plant shippers find it advantageous to maintain, for example, expensive flowers at a 10.degree. C. (50.degree. F.) temperature to avoid premature blossoming. Various other shippers and producers require that their product be retained at a particular temperature for optimum results.
In the distribution of various materials it is difficult to maintain an unbroken chain of refrigeration (or heating when products are in a colder climate) such that the storage material retains the predetermined optimum temperature. Moreover, it is often desirable to ship simultaneously a variety of materials having different optimum temperatures. Because of the differences in optimum temperatures, however, the products either have to be shipped separately, shipped together at a compromise temperature (which can lead to losses due to product degradation), or placed in separate containers with their own cooling or heating device (which leads to added shipping costs, complexity and the possibility of one type of cooling/heating means adversely affecting a neighboring storage container).
For example, a distributor might desire to transport to a specific location a load of frozen shrimp and live lobsters. Attempts to maintain the shrimp frozen could lead to the death of the live lobsters, while attempts to maintain the lobsters at an optimum transport temperature (e.g. 4.5.degree. C. or 40.degree. F.) could lead to undesirable thawing of the frozen shrimp. Hence, to avoid destruction of the load and an unhappy recipient, the distributor is likely to ship separately or spend additional labor and money in attempting to position and individually refrigerate the two types of loads in a single freight carrier.